Over the recent years, a telephone network built up by an existing circuit switching technology has been replaced with an IP (Internet Protocol) packet-based communication network using a packet switching technology. With this transition, a layer-2 backbone transmission system is gradually replaced with an Ethernet (registered trade mark)-based transmission system exhibiting high compatibility with the IP packet. The backbone circuit is requested to accommodate large-capacity lines and to have a fault tolerance. Devices, which support the packet switching network, adopt a new Ethernet (registered trade mark)-based technology and are underway to follow the conventional large-capacity accommodation and fault tolerance so as to satisfy the market demands.
A link aggregation, a “1+1 switching” technique and a “1:N switching” technique are exemplified as a main signal redundancy-structuring means that is generally employed in a packet forwarding device (which is termed a [packet device] as the case may be) accommodating such a large capacity of lines.
The link aggregation is a technology by which a plurality of physical lines is virtually bundled as if treating one single line. The link aggregation is defined by IEEE802.3d.
The use of the link aggregation enables a quantity of bands, into which specific bands of the physical lines are totaled, to be employed. For example, when five lines each having 1 Gbps are virtually bundled, a 5 Gbps virtual communication band can be employed. The communication band can be expanded without preparing a high-speed line by making use of the link aggregation. This scheme enables a flexible and efficient network to be designed. Therewith, there is redundancy in which when a trouble occurs in one of the physical lines, the communication can continue by use of another line.
FIG. 11 illustrates an example of a block diagram of the packet forwarding device. In FIG. 11, a packet device 100 includes a main signal unit 200 and a monitor control unit 300 that monitors and controls the main signal unit. The main signal unit 200 includes a plurality of interface terminating units 500 and a switch unit 400 which forwards a packet to an output port.
The packet forwarding device 100 is, in terms of reducing an initial introduction cost and taking a parts packaging area into consideration, constructed of a plurality of card-type circuit units according to functions such as the monitor control unit 300, the switch unit 400 and the interface terminating units 500.
FIG. 12 is a diagram illustrating one example of a general method (which is referred to as a method 1) of determining a link aggregation route when configuring the link aggregation in the packet forwarding device 100.
In FIG. 12, a port (Port) #1 of a card (Card) X defined as the interface terminating unit 500x and a port #1 of a card Y defined as the interface terminating unit 500y belong to a single link aggregation group. When the packet, which should be forwarded to this link aggregation group, is input to a card A defined as the interface terminating unit 500a on an ingress (Ingress) side, the card A determines which port, the port #1 of the card X or the port #1 of the card Y on an egress (Egress) side, the packet should be forwarded to, and forwards the packet to only any one of the ports. In the example illustrated in FIG. 12, the packet is forwarded to the port #1 of the card X. Thereafter, the packet is forwarded to the card X via the switch unit 400 and is output from the port #1 of the card X.
FIG. 13 is a diagram illustrating one example of a general method (which is referred to as a method 2) of determining the link aggregation route in the case of configuring the link aggregation in the packet forwarding device 100.
The method 2, unlike the method 1 by which the ingress interface terminating unit 500 determines a forwarding destination port to which the packet is output, is a technique of forwarding the packets to all of the interface terminating units 500 included by the link aggregation group and discarding the packets that are not forwarded by the egress interface terminating unit 500.
In FIG. 13, the link aggregation group is organized by the port #1 of the card X defined as the interface terminating unit 500x and the port #1 of the card Y defined as the interface terminating unit 500y. When the packet, which may be forwarded to this link aggregation group, is input to the card A as the ingress interface terminating unit 500a, the card A forwards this packet to the switch unit 400. The switch unit 400 copies the packet and forwards the packets to both of the card X and the card Y on the egress side. The card X and the card Y on the egress side determine whether the received packet is to be output to the external line or discarded, and executes the determined process. In FIG. 13, the card X outputs the packet to the external line, while the card Y discards the packet.
Thus, the link aggregation route determination scheme based on the method 2 is that the switch unit 400 copies the packet and forwards the same packet to all of the egress interface units 500 of the link aggregation group, and the egress interface units 500 determine which the packet is output to the external line or discarded.
In comparison between the method 1 and the method 2, the method 2 is that the switch unit 400 forwards the packet to all of the interface terminating units 500 corresponding to the redundancy-structured lines. Therefore, a band between the interface terminating unit 500 scheduled to discard the packet and the switch unit 400 gets futile.
The method 1 is that the ingress interface terminating unit 500 determines the output port for the packet, and the packet is forwarded to only the interface terminating unit having this output port. Hence, the futility of the band in the case of applying the method 2 does not occur. Accordingly, in the case of performing the link aggregation, generally the method 1 is applied.
The method 1 has, however, the following problem. FIG. 14 is an explanatory diagram illustrating the problem inherent in the method 1. In FIG. 14, the port #1 of the interface terminating unit #4 (IF#4) and the port #1 of the interface terminating unit #5 (IF#5) belong to the same link aggregation group.
According to the method 1, the ingress interface terminating unit 500 determines the destination route for the packet. Therefore, all of the interface terminating units 500 in the packet device 100 need to know a status of the destination route in order to make a proper determination.
Accordingly, when a fault occurs in the link related to one (for example, the port #1 of IF#4) of the ports belonging to the link aggregation group, what is requested is to notify all of the interface terminating units 500 including IF#4 of such a piece of information that the fault has occurred in the link of the port #1 of IF#4.
In an example of FIG. 14, the interface unit IF#4 notifies the monitor control unit 300 of the link fault occurring at the port #1 ((1) in FIG. 14), and the monitor control unit 300 notifies all of the interface terminating units 500 of the fault occurring at the port #1 of IF#4 ((2) in FIG. 14). Each interface terminating unit 500, when receiving the notification from the monitor control unit 300, changes the setting about the should-be-determined output port so as not to forward the packet addressed to the link aggregation group to the port #1 of IF#4 ((3) in FIG. 14). FIG. 14 illustrates an example of forwarding the information via the monitor control unit 300. Even when forwarding the information by another method, all of the ingress interface terminating units 500 have to be notified of the fault information. Accordingly, the number of the fault notifying destinations rises as the number of the interface terminating units 500 increases.
The respective interface terminating units 500 are notified of the link fault not in parallel but serially in terms of a structure of the device. In this case, for example, such a status of switching transit period exists that the notification of the fault about IF#1 and the setting update based on this notification have been completed, while even the notification of the fault about IF#6 is not yet made. As the number of the link fault notifying destinations rises, the status of the switching transit period gets elongate, and the time expended for switching increases.
As described above, according to the method 1, when the fault occurs in the output destination, it is requested that all of the interface terminating units within the packet forwarding device be notified of the fault information. Accordingly, as a capacity of the lines accommodated in the device increases, the time requested for switching gets elongate. In recent years, an improvement of reliability is requested of the IP packet-based communications. Hence, it is desirable to reduce the time required for switching. Note, this request is not limited to IP packet-base communications and occurs in the communication using the technique of redundancy-structured transmission routes.    [Patent document 1] Japanese Patent Laid-Open Publication No. 2003-318983    [Patent document 2] Japanese Patent Laid-Open Publication No. H11-163926